Academician Guo Guangcan’s team at the University of Science and Technology of China has made important progress in the research of non-local quantum networks, and the research team of Li Chuanfeng and Liu Biheng has cooperated with Dr. Armin Tavakoli of Austria and others to use super-entanglement to achieve entanglement exchange based on symmetric joint measurements, and to study the non-locality of the double-local Bell inequality and the full quantum network. The results were published in the Physical Review Letters on July 13.
Schematic diagram of the experimental principle, symmetric joint measurement on qubits 2 and 3 for the research group to provide pictures
The Belfi local domain is an important foundation for quantum mechanics and quantum information science. For more than a decade, research on non-locality has shifted beyond the two-body problem and has shifted to more complex structures. Such experiments involve multiple independent entanglement sources, which are distributed and measured in multiple parties and eventually form a non-local quantum network. Since the non-locality demonstrated by quantum networks breaks through the framework of traditional Bell experiments, there are huge challenges in both physical theory and experimentation.
At present, the entanglement measurement of independent entanglement sources connected in experiments mainly uses standard Bell state measurements, and there is still a lack of research on the properties of more general entanglement measurements and the non-local quantum networks they have established. Symmetrical joint measurements are an important class of entanglement measurements that are fundamentally different from Bell state measurements. It has elegant and natural symmetry and can be utilized as a quantum information resource. Arbitrary symmetric joint measurements require cascading operations of controlling non-gates and controlling phase gates, which poses a great challenge to linear optical quantum networks that can only probabilistically implement control gates between different photons.
In the experiment, the research team first prepared a super-entangled pair, and the states of the two photons produced were entangled in the polarization degrees of freedom and path freedom, respectively. Then, the polarization degrees of freedom and path freedom of the same photon are made arbitrarily symmetrically combined measurements through a universal quantum circuit. Since deterministic control gates can be achieved between different degrees of freedom of the same photon, the research team achieved arbitrary symmetrical joint measurements through the determinism of the polarization-path exchange device designed by itself. Experimental results show that the fidelity of symmetrical joint measurement achieved by the research group reaches 97.4%.
The research team used symmetric joint measurements to achieve entanglement exchange, and studied the double-local Bell inequality and the non-locality of the full quantum network. The experimental results show completely different properties from non-local quantum networks measured in the standard Bell state.
This achievement takes the first step beyond the non-local quantum network based on standard Bell state measurements, and proves that different entanglement measurements will construct non-local quantum networks with different advantages, providing a technical route for building non-local quantum networks with different structures. (Source: China Science Daily Wang Min)
Related paper information:https://doi.org/10.1103/PhysRevLett.129.030502